— reviewed against the regs as they stand.
Every fuel carries a carbon factor
SAP converts every kWh your dwelling uses into CO₂ and primary energy using fuel-specific factors. Your target (TER) is set by a notional dwelling using mains gas — so fuels with worse factors than gas start at a disadvantage that must be clawed back elsewhere.
The SAP 10 shake-up
Under SAP 2012, grid electricity carried a carbon factor 2.4× that of mains gas — making all-electric new builds notoriously hard to pass. SAP 10 cut electricity’s factor from 0.519 to 0.233 kgCO₂/kWh, barely above gas (0.210), reflecting today’s cleaner grid. Direct electric heating is now viable in the calculation — and a heat pump, delivering 3+ units of heat per unit of electricity, comfortably beats gas on carbon.
Practical implications
Mains gas remains the baseline the targets assume — but with the Future Homes Standard phasing fossil-fuel heating out of new builds, it’s a shrinking option. Heat pumps are now usually the strongest choice in SAP terms. Direct electric (panel heaters, electric boilers) passes more easily than before but high running costs still show in the calculation. LPG and oil carry worse economics and carbon, and typically need fabric or renewable compensation.
Choosing fuel early — before the design-stage SAP — avoids expensive redesign. If you’re undecided, we can model the options side by side. Ask us.